After installing and running the LoopMidi virtual port.
In vArranger : go to OPTIONS/MIDI PORTS, and select LoopMIDI in the MIDI OUT 1 list. (Select the GM2 mode)
In SampleTank standalone : go to the midi options, and select LoopMIDI in the MIDI IN list
This way, you connect a "cable" between the midi output of vArranger to the midi input of SampleTank